My newer Sylvania LC195SL8 suddenly. My newer Sylvania LC195SL8 suddenly has no sound on 4

Question

My newer Sylvania LC195SL8 suddenly has no sound on 4 channels. I've re-booted, disconnected the dvd player, re-set the channel scanner multiple times. Two other televisions on the same Comcast cable service are working fine. Do I need to make use of the warranty or is there something else I can try?